Aluminum Joints Research Articles

Investigation on the influence of FSP parameters on TIG welded dissimilar aluminum joints using RSM and desirability function approach

The present study aimed to explore the cumulative influence of friction stir processing (FSP) parameters, viz., tool spindle speed, traverse speed, and tool tilt angle, on the ultimate tensile strength (TS), ultimate flexural strength (FS), microhardness (MH), and wear rate (WR) of tungsten inert gas (TIG) welded dissimilar AA6061-T6 and AA7075-T6 alloy joints. A face-cantered central composite design (FCCCD) of response surface methodology (RSM) was adopted to design the experiments. Analysis of variance (ANOVA) was employed to identify the significant factors and interaction effects. Multi-response optimization was performed using the desirability function approach to identify parameters that maximize TS, FS, and MH and minimize WR. A confirmation study under optimal conditions were also carried out. FSP significantly improved the TIG joint properties by producing more homogeneous and refined grains (average grain size of 7.75 µm) without any weld defects. The TS, FS, and MH of TIG welds have increased by 66.87%, 61.95%, and 69.01%, respectively, while the WR decreased by 37.87% after FSP. The fractography revealed that TIG welds lead to a brittle failure mode, and the FSP + TIG welds showed a ductile failure mode. The tool spindle speed was the most influential factor affecting joint properties. With increased spindle speed, the TS, FS, and MH of the joint increased, while the WR decreased. At a spindle speed of 1300 rpm, a traverse speed of 50.75 mm/min, and a tilt angle of 1.76°, the optimum TS of 271.89 MPa, the FS of 298.03 MPa, the MH of 122.23 HV, and the WR of 77.48 µm were observed.

Finite element modeling of quasi-static failure of aluminum joints with titanium bolts and liquid shim

Liquid shims are often used to fill tolerance gaps between bolted joint plates in aircraft structures. This paper presents an experimental and numerical study of the effect of liquid shim and pretension on the quasi-static behavior of aluminum joints with titanium bolts. Single shear butt joint specimens with and without liquid shim, and with two levels of bolt pretension, were tested to failure. The experiments were simulated using FE-models which include elastic–plastic material behavior and a ductile damage model. Both the simulations and the experimental tests showed that the level of pretension had a small effect on the failure load. On the other hand, the specimens with liquid shims had a significantly lower strength and stiffness than the specimens without the shims.

Microstructure and Mechanical Properties of Electrically Assisted Brazing Joints of Dissimilar Aluminum and Steel Alloys

The microstructure and mechanical properties of electrically assisted brazing (EA-brazing) joints of aluminum alloy 6061-t6 (AA6061-t6) and S45C steel are experimentally investigated. During the EA-brazing process, an electric current is directly applied to the cylindrical specimen assembly (S45C and AA6061-t6) and fillers of 88% Al and 12% Si (in the middle of the specimen assembly). The temperature of the specimen assembly rises rapidly to the melting point of the filler and remains nearly constant for a period of time using a pulsed electric current. Two types of EA-brazing joints are fabricated, namely Joint-0s (no temperature holding time) and Joint-12s (12 s temperature holding time). The characteristics of the intermetallic compounds (IMCs) formed at the EA-brazing joint interface are analyzed using scanning electron microscopy and energy dispersive spectrometer. Compared to Joint-0s, the Fe-rich IMCs (FeAl) are observed at the interface of Joint-12s due to the 12 s temperature holding time. In addition, the microstructural analysis shows that the thickness of the diffusion layer increases with increasing temperature holding time. The mechanical properties of the EA-brazing joints are evaluated using bending tests. The results of the mechanical test show that the strength of Joint-12s is higher than that of Joint-0s.

Metallurgical characteristics of AA6061 aluminium and AZ31B magnesium dissimilar joints by fusion welding technique.

Aluminium (Al) and magnesium (Mg) alloys are extensively used in the automobile sector because of their high strength-to-weight ratio, excellent castability low density and simplicity of recycling. Al-Mg structures used in the automotive sector can potentially reduce their weight. Although there is a significant opportunity for substantial cost reduction, the use of magnesium in aluminium structures remains restricted. This study aims to weld 3 mm-thick rolled sheets of AA6061 Al and AZ31B Mg alloy using the cold metal transfer (CMT) arc welding process. Three different filler wires (ER1100, ER4043, and ER5356) were used in the experiment. In this article, the mechanical and microstructure characteristics of Al/Mg dissimilar joints manufactured by CMT are evaluated and discussed in detail. Optical microscope (OM), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and x-ray diffraction (XRD) were used to analyze the CMT-welded Al/Mg dissimilar joints. Of the three filler wires used, ER4043 (Al-5%Si) filler wire yielded defect-free sound joints due to the presence of Si, which improves the flow ability of molten filler during welding. The presence of Mg-rich intermetallics-Al12Mg17)and Al-rich intermetallics-Al3Mg2 were observed. The fractured area of the CMT-welded Al/Mg dissimilar joints revealed the presence of the Mg-rich intermetallics (Al12Mg17), which is responsible for the decrease in tensile strength. The reduction of intermetallics, particularly of Mg-rich intermetallics (Al12Mg17) is important for improving joint strength. RESEARCH HIGHLIGHTS: Cold metal transfer (CMT) arc welding was used to control the Al-Mg-rich intermetallics in the Al/Mg dissimilar joints. The microstructure, morphology and phase composition of the welded joints were studied by OM, SEM, TEM, EDS and XRD. The weld metal and AL substrate bonded with a strong interface, while weld metal and Mg substrate were joined at the epitaxial solidification area where the intermetallic compounds of Mg2Al3, Mg17Al12 and Mg2Si are generated. The weld metal on the Mg side experienced brittle fracture, with a continuous distribution of Mg2Al3, Mg17Al12 and Mg2Si.

Development of FSW Process Parameters for Lap Joints Made of Thin 7075 Aluminum Alloy Sheets.

The article describes machine learning using artificial neural networks (ANNs) to develop the parameters of the friction stir welding (FSW) process for three types of aluminum joints (EN AW 7075). The ANNs were built using a total of 608 experimental data. Two types of networks were built. The first one was used to classify good/bad joints with MLP 7-19-2 topology (one input layer with 7 neurons, one hidden layer with 19 neurons, and one output layer with 2 neurons), and the second one was used to regress the tensile load-bearing capacity with MLP 7-19-1 topology (one input layer with 7 neurons, one hidden layer with 19 neurons, and one output layer with 1 neuron). FSW parameters, such as rotational speed, welding speed, and joint and tool geometry, were used as input data for ANN training. The quality of the FSW joint was assessed in terms of microstructure and mechanical properties based on a case study. The usefulness of both trained neural networks has been demonstrated. The quality of the validation set for the regression network was approximately 93.6%, while the errors for the confusion matrix of the test set never exceeded 6%. Only 184 epochs were needed to train the regression network. The quality of the validation set was approximately 87.1%. Predictive maps were developed and presented in the work, allowing for the selection of optimal parameters of the FSW process for three types of joints.

Effect of Different Step-Lap Joints on the Natural Frequencies of Different Adhesively Bonded Metallic Materials: A Numerical Study

Due to their many applications' benefits, adhesively bonded joints are widely utilized in nearly every industry, including space, marine, automotive, and aeronautics. Since unpredicted loadings may cause resonance in the structures, an accurate prediction of the bonded joints' dynamic characteristics is crucial. Therefore, in this study, modal analysis was performed on the two-, three-, four- and double-step adhesively bonded lap joints of Aluminum (Al), Copper (Cu), and Mild steel (Ms) materials with Epoxy Araldite adhesive. Ansys commercial program was utilized to analyze it numerically. The results showed that modeling the bonding region of single lap joints as two-, three-, and four-step adhesively bonded lap joints has no significant effect on the natural frequencies. This modeling has a minor incremental effect on the natural frequencies. However, Double-step lap joints were found to cause a considerable reduction in natural frequencies compared to not only single lap joints but also two-, three-, and four-step adhesively bonded lap joints. Double-step bonding caused a decrease of 8.82%, 8.57%, and 8.73% for Al-Al, Cu-Cu, and Ms-Ms. In general, in all models, the best increase or decrease in terms of natural frequencies was found to be Cu-Cu adhesively lap joints.

Study on microstructure evolution and mechanical properties of similar joint of Al-Mg-Si alloy by tungsten inert gas welding

Aluminium alloys are widely used to structural material purposes, there is sometimes the welding processes are needed to join this material. One of the promising welding methods are Tungsten inert gas (TIG) can be used to join of similar or dissimilar aluminium. Their qualities are influenced by correct selected of the weld parameters. The inert gas, filler rod, heat treat, and current intensity are such important parameters. The aim of this research to investigate mechanical properties and microstructure evolution with varying welding current. In the present work the similar joint of the A6061 aluminium was carried out by TIG method by using ER 5356 filler rod, and current intensities (90A, 100A, and 110 A). The hardness and tensile strength obtained through micro Vickers and universal testing machine respectively at room temperature. The microstructure observation at heat effected zone and weld metal area with optical microscope was conducted. The results show that the TIG was successful to join A6061 which is the maximum 243 MPa of ultimate tensile strength and ±104 HV hardness acquired. It was clearly observed that the weld metal area has a finer grain as weld processes with 110 A current in comparison with other current intensities.

Joining Mechanism of Resistance Spot Welded Joints of Aluminum Casting Alloy and 6000 Series Rolled Aluminum Alloy

Joining Mechanism of Resistance Spot Welded Joints of Aluminum Casting Alloy and 6000 Series Rolled Aluminum Alloy

Inhibition study of curcumin extract’s effect on dissimilar aluminium joint

Aluminium welded joints are offering greater interest to researchers owing to the replacement of heavy steel structures and reduction in the weight of the components used in the automobile and marine environments. In this study AA6061 and AA8011 have been welded by using the bobbin tool friction stir welding method and by varying the process parameters with the samples being subjected to corrosion environments. The corrosive nature of the welded alloys in the absence and presence of inhibitors (curcumin) has been examined by electrochemical methods and compared with raw samples. The ratio has been observed between 0.075 and 5.42 A cm-2. The results reveal that corrosion control tendency has been improved by the AA6061 and AA8011 aluminium alloy joint in the presence of curcumin extract.

Investigation of low-cycle fatigue in adhesively-bonded single-lap joints

Adhesively bonded joints are used as an alternative to classical mechanical joining methods, e.g., bolts, rivets, welding, and soldering, due to their advantages such as high strength, uniform stress distribution, and good fatigue resistance. These adhesively bonded joints are becoming more and more important, especially in fields where weight is critical, such as aviation and aerospace. Adhesively bonded joints are preferred because they offer highly reliable connections. In the present study, the low-cycle fatigue of materials joined together as adhesively bonded single-lap joints were investigated experimentally and numerically. Joints of aluminum and steel samples were subjected to variable loads that were lower than the experimentally obtained average breaking loads, and the number of cycles was determined. As a result, the fatigue life of adhesively bonded single-lap stainless steel samples was observed to be higher than that of aluminum samples. In addition, it was also observed that smudging adhesive around the endpoints of the joint significantly increased the fatigue life of steel samples.

Behaviour of aluminium/steel hybrid RSW joints under high cycle fatigue loading

The lightweight construction of automotive car bodies is the more important to reduce the fuel consumption and costs. High-strength steels and aluminium alloys are suitable for achieving these aims. Recent car bodies contain both materials, therefore necessary to make reliable joints between them. The resistance spot welding (RSW) can be used for joining of car bodies and it is applicable for aluminium/steel hybrid joints, too. High cycle fatigue (HCF) test results can be rarely found in the literature while HCF loading basically determines the lifetime of hybrid joints. 5754-H22, 6082-T6, and DP600 base materials were used for similar and hybrid RSW joints and HCF tests were performed. Number of cycles to failure values, failure modes, furthermore brittle intermetallic compound (IMC) layers were studied and analysed. In both aluminium/steel hybrid joints, the HCF test results showed better endurance limit like concerning aluminium/aluminium similar joints, but worse than steel/steel joints. For 5754-H22 alloy the endurance limit values are 648 N, 939 N, and 1285.5 N, for similar aluminium, hybrid, and similar steel joints, respectively. For 6082-T6 alloy these values are 513 N, 625.5 N, and 1285.5 N, respectively. In case of similar joints only base material fracture happens, but hybrid joint specimens show different failure modes. Base material fracture and shearing after partial base material fracture were typical failure modes in case of 5754-H22/DP600 and 6082-T6/DP600 hybrid joints, respectively. The full and partial plugging as a failure modes appeared for hybrid joints, too. The IMC layer characteristics showed opposite results in cases of hybrid joints, both the layer thicknesses of the shared and plugged joints and the thickness differences between the inner and outer parts of the joints were different.

The effect of chemical etching and nanostructure additive epoxy coating technique on adhesion strength in aluminum joints bonded with nanostructure additive adhesive

In the present study, in order to increase the strength of adhesively bonded joints, the surface of the adherend was chemically etched with an anodizing treatment process at different temperatures and the surface was coated with nanostructure doped epoxy. Additionally, carbon nanostructures were added to the adhesive at different ratios to increase the strength of both the adhesive and the joint. In the study, in order to clean the surfaces of AA2024-T3 aluminum alloy plates and eliminate the oxide layer, the plates were chemically treated with a sodium hydroxide solution. Afterwards, the surfaces of these aluminum alloy plates were chemically etched with an anodizing treatment process at temperatures of 25, 40 and 60 °C. The aim here is to create different surface roughness and surface energy on the aluminum alloy surface. Epoxy pre-coating (EPC) was applied to the chemically etched aluminum alloy surfaces. Furthermore, a single-lap joint was produced by adding 0.5 %, 1 % and 2 % carboxylated carbon nanotube (CNT-COOH) by weight to the EPC and adhesive applied to the surfaces and the failure loads of the joints were examined. As a result, when the failure load obtained from the experiments was examined, it was found that chemical etching alone increased the joint strength by 22 % while the chemical etching and EPC application increased it by 46 %, the chemical etching and nanostructure doped EPC application increased it by 61 % and nanostructure addition to the adhesive increased it by 93 %. However, these increases in joint strength vary depending on the duration of the anodizing treatment process and the nanostructure additive ratio. In the chemical analyses performed to interpret these results, surface roughness test, surface contact angle test, X-ray photoelectron spectroscopy (XPS), fourier-transform-infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and images obtained from the failure surfaces were used, respectively.

A novel epoxy adhesive with metal organic framework (MOF) and poly(butyl acrylate‐block‐styrene) for bonding aluminum–aluminum joints: A complete overview of mechanical, thermal, and morphological properties

AbstractIn this study, MIL‐101 (Cr) and NH2‐MIL‐101 (Cr) nanoparticles were synthesized by hydrothermal method. Butyl acrylate‐styrene copolymer was used along with these nanoparticles to improve the mechanical properties of epoxy adhesive. The results of the Fourier Transform Infrared (FTIR) and X‐ray diffraction (XRD) test showed that the synthesis and functionalization of the metal organic framework (MOFs) were successful. The mechanical properties and adhesion features in the lap joint bonding of aluminum foil to the aluminum foil of modified epoxy adhesives were investigated by tensile and lap shear tests. The results of the tensile test showed that by adding 0.3 wt% of NH2‐MIL‐101 (Cr) and 2.5 wt% of poly(butyl acrylate‐block‐styrene) to epoxy adhesive, the tensile strength, modulus and toughness of dumbbell samples were increased up to 34.46%, 31.74% and 58.53%, respectively. Furthermore, based on the lap shear test results, by adding 0.3 wt% NH2‐MIL‐101 (Cr) along with 2.5% poly(butyl acrylate‐block‐styrene) to the epoxy adhesive, the lap shear strength of samples increased from 1.05 ± 0.08 MPa to 5.25 ± 0.06 MPa compared to the neat epoxy adhesive. According to the TGA test, the highest thermal stability is related to the sample containing 0.3 wt% of NH2‐MIL‐101 nanoparticles and 2.5 wt% of the copolymer. The image of the fracture surface of the sample containing 0.3 wt%. NH2‐MIL‐101 (Cr) and 2.5 wt% block copolymer shows that the interface of nanoparticles and the matrix improved due to the chemical reaction of functional groups of nanoparticles and adhesive matrix.

Joining of Polymer to Aluminum Alloy AA1050 By Friction Spot Welding

The friction spot welding process is used to join the hybrid joint of aluminium to polymer. AA 1050 Aluminum alloy and polyethylene polymer (type of plastic) were used for joining. Aluminium surface treatment was done to increase the wettability of it. The surface treatment was done by electrochemical treatment. Two parameters of the joining process were used: (1, 1.5 and 2) min. (920, 1340 and 1500) rpm for time and rotational speed, respectively. Many tests for the joint are done: shear test and Scanning electron microscopy (SEM). Using the Minitab program, the effect of the parameters on the joint was analysed. The maximum value of the shear force was (1587 N) at 1.5 min. time and 1340 rpm rotational speed. The minimum shear force was (589 N) at 1 min. time and 920 rpm rotational speed. The joints which were tested failed by an interfacial shear with a ductile fracture of the polymer side. The process of joining mechanism occurred through a mechanical interlocking between the molten polymer and the surface of the AA 1050 aluminium specimen, cohesive and adhesive. The average thickness for the joint of the tested specimens was 4µm.

Contact acoustic nonlinearity and local damage resonance for the detection of kissing bonds in structural adhesive joints

Adhesively bonded joints are susceptible to contamination of surfaces during manufacture and environmental deterioration in real operating conditions. These may cause the generation of so-called “kissing bonds” that can dramatically alter the strength of the joint leading to premature failure. Nonlinear acousto-ultrasonic (AU) techniques have shown great potential for monitoring kissing bonds with piezoelectric sensors permanently installed on the structural joint, thus enabling online and in-situ inspection. This paper investigated the combined contact acoustic nonlinearity (CAN) and local damage resonance (LDR) effects in the presence of kissing bonds in adhesive joints. Experimental nonlinear AU tests showed the formation of LDR frequency down-shifts and “jumps” of the fundamental damage resonance in adhesively bonded aluminium joints, with the kissing bond located internally to the overlapping region between the two adherends. These results were supported by a theoretical model based on the solution of the nonlinear Duffing's equation, under the assumption that the debonded region is a damped nonlinear harmonic oscillator subject to harmonic forcing. The Harmonic Balance Method was used to solve the nonlinear differential problem, showing the generation of frequency down-shifts via the dependence of the ratio between the excitation and LDR frequencies with the amplitude of the fundamental damage resonance. Additionally, two-dimensional finite element simulations using a reduced order model based on the Craig-Bampton technique were carried out to support experimental AU tests for the identification of the LDR frequency and the generation of nonlinear resonance effects. Good agreement between analytical, numerical, and experimental results revealed that a monitoring approach combining CAN and LDR is an extremely efficient and sensitive tool for ensuring integrity and safety of structural adhesive joints.

Creep failure analysis of crimp joints in aluminium and copper windings of distribution transformers

The present work investigates creep performance and contact resistance of Distribution Transformers (DTs) winding crimp joints under the influence of temperature and stress, aiming to reduce the failure rate of DTs. The integrity of crimp joints is crucial, as the field study revealed that a majority of crimp joints become unstable and show elevated contact resistance due to service exposure. These changes affect the steady-state creep rate of the crimp joint and the surrounding winding conductors, ultimately diminishing the operational lifespan of DTs. For experimentation, crimp joints with varying crimp points were fabricated for a 25 kVA DT using aluminium and copper conductors with diameters of 0.83 mm and 0.6 mm, respectively. For all types of joints i.e., Al-Al, Al-Cu and Cu-Cu, the 2-point crimp joint was identified as optimum in terms of tensile strength and contact resistance. The creep tests for the crimp joints were conducted under varying temperatures of 100 °C and 140 °C with stress levels of 40 MPa and 55 MPa as per ASTM E139-11. The steady-state creep rate and contact resistance of Al-Al crimp joints increased with an increase in temperature and stress. The creep life of DTs due to Al-Al and Al-Cu crimp joints is significantly less than the designed life of a typical DT. On the other hand, creep behaviour of copper winding crimp joints supports a significantly higher DT creep life even at a higher temperature of 140 °C and elevated stress of 55 MPa.

Accelerating environmental ageing effects of adhesively bonded aluminium joints by using smaller bonding areas

ABSTRACT In all areas of application, adhesive joints are exposed to environmental conditions, which can weaken the joint. To verify the functionality of the joints for a certain service life, accelerated ageing tests are used. To assess the mechanical performance of aged joints, single lap joints (SLJ) are often used. The influence of various geometries of SLJ on the strength and stress behaviour is known. The various ageing processes in bonded joints are not yet sufficiently known. Thus, the influence of the specimen geometry on the ageing behaviour cannot be reliably estimated and is therefore investigated in this work. SLJ with different geometries made of an AlMgSi alloy and a one-component epoxy-hybrid adhesive were artificially aged. T dimensions of the SLJ were varied in width, overlap length, adhesive thickness or joint design. Similar ageing results were seen in a significant shorter time with narrower samples or shorter overlap length. A SLJ with a bonding area of 6.3 mm x 6.3 mm was derived from these results. After 4–5 weeks of ageing, this shows comparable results to the standard test SLJ after 8 weeks. This allows to speed up industrial ageing tests nearly by factor two without changing ageing mechanisms.

Influence of Strain Rate on Metallurgical and Mechanical Properties of Friction Stir Spot Welded Aluminium Joints

Nowadays, the substitution of copper with aluminium is widely pursued in order to save weight and material costs, for battery components and wire connectors. Additionally, cost reductions can be further enhanced with effective reduction of energy consumption through efficient manufacturing. Therefore, friction stir spot welding as a solid-state welding technique is a potential choice with low energy demands and high joining performances. However, the joining of aluminium and its alloys with solid-state welding techniques is still a challenging task due to a persistent and chemically stable aluminium oxide layer formed at the sheets prior to the welding, due to the reaction between aluminium and atmospheric oxygen. In this paper, the influence of strain rate induced during friction stir spot welding process on the metallurgical, mechanical and electrical properties of friction stir spot welding of AA 5754-H111 was studied. The strain rate was calculated according to the rotational speed of the tool and the effective (average) radius and depth of the stir zone. It was observed that the specimens welded with a lower strain rate endured a 15 % higher average strain failure load compared to the specimens welded at a higher share rate. The microhardness profiles of the specimens obtained at low strain rates imply strain hardening mechanisms in the weld zone, while the microhardness of specimens welded at high strain rates expressed thermal softening. It was also found that the friction welded sheets, regardless of the strain rate, show increased electrical resistance compared to the base material, however, it decreases with an increase in strain rate. Microstructural analysis reveals a stress-induced metallurgical transformation in the narrow zone around the weld-faying interface.

Tool Rotational and Tool Travel Parameters Influence On Friction Stir Welded Dissimilar Joints Properties

Present work is to examine the effects of tool rotational and tool travel parameters on Friction Stir Welded (FSW) dissimilar joints mechanical and microstructural characteristics for 3 mm thick pure copper and 6061 aluminium alloy plates. Welds were made with a cylindrical tapered pin to achieve this goal. The tool rotational speed and tool travel speed are the primary FSW factors considered in this study. Copper plates were kept on the joint's advancing side. Tensile and bending tests are carried out to assess the tensile and bending strength of weld joints in accordance with ASTM standards. Vicker's microhardness tests were carried out in the transverse direction of the weld to check the hardness distribution in weld nuggets. An experimental analysis shows that the best tensile strength 98 MPa and bending stress 16.6 MPa are achieved at tool rotating speeds of 1000 rpm and 62 mm/min, correspondingly. The larger concentration of copper particles in the aluminium region is mostly to blame for this. For 1400 rpm and 62 mm/min, a nugget zone hardness of 190 HV is attained. The presence of more Cu particles on the Al side is evident in SEM pictures, and the higher tensile and bending strength is mostly attributable to the Cu particles covering the Al material in the weld zone. According to X-ray analysis, the synthesis of intermetallic complexes such Al4Cu9, Al2Cu, AlCu, and AlCu4 explains the chemical reaction and phase transformation at the interfaces. The maximum strength values improved because of these intermetallic compounds' proper metallurgical bonding and thinnest thickness. According to fracture analysis, joints with higher strengths have intergranular fracture, while joints with lower strengths experience brittle fracture on both aluminium and copper joints.

Investigation of the influence of the loading arrangement on the measured mode-I fracture resistance

This paper investigates the influence of the loading arrangement of double cantilever beam (DCB) test on the computed fracture resistance parameters of a structural adhesive. Aluminium joints were tested on three conventional loading arrangements from the BS ISO 25217:2009. We have found that the compliance of different loading arrangements can lead to significant differences in the fracture resistance computed using the cross-head displacement of the tensile-testing machine, even after considering the take-up of play and machine-compliance effects. In contrast, using the digital image correlation to measure the load-line displacement results in fracture resistance that is essentially independent of the loading arrangement. This finding was confirmed using three different data-reduction schemes, which yielded almost identical values of fracture resistance (less than 1% difference). Furthermore, direct identification of the traction-separation law at the crack tip was performed using Savitzky–Golay filter to compute the derivative of the J integral with regard to normal separation. Again, no significant influence of the loading arrangement was found since identified values of the separation at the peak traction and maximum separation are in excellent agreement. The identified maximum separation can be used as a threshold value of the relative deflection of the DCB arms to automatically determine the crack-tip position.